While the utility of zeolite P in detergent formulations has been acknowledged, for example in European Patent Application 0384070 (Unilever), they must be manufactured by a commercially effective process in order to become available on the market place. Thus, while the properties of a material may make it a useful commercial commodity, its manufacture has to be optimised for large scale production.
The zeolite P class includes a series of synthetic zeolite phases which may be in cubic configuration (also termed B or P.sub.c) or tetragonal configuration (also termed P.sub.1) but is not limited to these forms. The structure and characteristics of the zeolite P class are given in "Zeolite Molecular Sieves" of Donald W Breck (published 1974 and 1984 by Robert E Krieger of Florida USA). The zeolite P class has the typical oxide formula: EQU M.sub.2/n O.Al.sub.2 O.sub.3.1.80-5.00 SiO.sub.2.5H.sub.2 O
M is an n-valent cation which for this invention is an alkali-metal, that is lithium, potassium, sodium, caesium or rubidium with sodium and potassium being preferred and sodium being the cation normally used in commercial processes.
Thus sodium may be present as the major cation with another alkali metal present in a minor proportion to provide a specific benefit.
In EP-A-565,364 is described a process for preparing P zeolites in which aluminate and silicate solutions are reacted in presence of P zeolite seeds. During the formation of the crystalline zeolite the reacted medium passes through a gel stage. This process enables the production of high quality detergent zeolites having a Calcium Effective Binding Capacity (CEBC) of above 146 mg/g, with outstanding Calcium Uptake Rate (CUR) and high oil absorption.
In some applications it can be considered to use detergent zeolites with lower detergent characteristics but high oil absorption.
In U.S. Pat. No. 3,112,176 is described a process in which P type zeolites are produced from metakaolin. Having reproduced the examples disclosed in this document, a maximum Calcium Effective Binding Capacity of 90 mg/g has been obtained. Moreover, the kinetics characteristics of these zeolites were found to be very poor with a Calcium Uptake Rate of above 500 seconds.
In U.S. Pat. No. 3,008,803 is described a process in which aluminium hydroxide, silicic acid and water are mixed in a vessel and allowed to react at 100.degree. C. for 48 hours with stirring. The agitation is stopped and the mixture is maintained at 100.degree. C. for an additional 71 hours. A P-type zeolite with a CEBC of 65 mg/g and a CUR of above 500 seconds was obtained.
Now, to be used in detergents applications, a zeolite must exhibit, on top of a good CEBC (at least 100 mg/g), a Calcium Uptake Rate of less than 100 seconds. Therefore the zeolites P disclosed in U.S. Pat. No. 3,112,176 and U.S. Pat. No. 3,008,803 are not suitable for detergent applications.
There is therefore a need for a P-type zeolite with good detergents characteristics (i.e CEBC above 100 mg/g and CUR below 100 seconds) intermediate between those disclosed in U.S. Pat. No. 3,112,176 on the one hand and those disclosed in EP0384070 on the other hand. For the time being, it has not been possible to obtain such a P-type zeolite.
It has now been discovered that it is possible to obtain such an intermediate zeolite.